1.\" Copyright (c) 2004 Michael Telahun Makonnen 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.Dd August 17, 2018 26.Dt PTHREAD_RWLOCK_TIMEDRDLOCK 3 27.Os 28.Sh NAME 29.Nm pthread_rwlock_timedrdlock 30.Nd "acquire a read-write lock for reading or give up after a specified period" 31.Sh LIBRARY 32.Lb libpthread 33.Sh SYNOPSIS 34.In pthread.h 35.Ft int 36.Fn pthread_rwlock_timedrdlock "pthread_rwlock_t *restrict rwlock" "const struct timespec *restrict abs_timeout" 37.Sh DESCRIPTION 38This function acquires a read lock on the read-write lock 39.Fa rwlock . 40However, if the lock cannot be 41acquired without waiting for another thread to 42unlock the lock, 43this wait shall be terminated when 44.Fa abs_timeout 45expires. 46.Pp 47A thread may hold multiple concurrent read locks. 48The 49.Xr pthread_rwlock_unlock 3 50function must be called once for each lock acquired. 51.Pp 52If the thread should be interrupted by a signal, 53the 54.Fn pthread_rwlock_timedrdlock 55function will be automatically restarted after the thread returns from 56the signal handler. 57.Pp 58The calling thread may deadlock if 59at the time the call is made it holds a write lock on 60.Fa rwlock . 61The results are undefined if this function is called with 62an uninitialized read-write lock. 63.Sh IMPLEMENTATION NOTES 64To prevent writer starvation, writers are favored over readers. 65.Sh RETURN VALUES 66If successful, the 67.Fn pthread_rwlock_timedrdlock 68function will return zero. 69Otherwise, an error number will be returned to indicate the error. 70.Pp 71This function shall not return an error code of 72.Er EINTR . 73.Sh ERRORS 74The 75.Fn pthread_rwlock_timedrdlock 76function will fail if: 77.Bl -tag -width Er 78.It Bq Er ETIMEDOUT 79The lock could not be acquired before the specified timeout expired. 80.El 81.Pp 82The 83.Fn pthread_rwlock_timedrdlock 84function may fail if: 85.Bl -tag -width Er 86.It Bq Er EAGAIN 87The read lock could not be 88acquired because the maximum number of read locks for 89.Fa rwlock 90would be exceeded. 91.It Bq Er EDEADLK 92The calling thread already holds a write lock on 93.Fa rwlock . 94.It Bq Er EINVAL 95The value specified by 96.Fa rwlock 97does not refer to an initialized read-write lock object, 98or the 99.Fa abs_timeout 100nanosecond value is less than zero or 101greater than or equal to 1 billion. 102.El 103.Sh SEE ALSO 104.Xr pthread_rwlock_init 3 , 105.Xr pthread_rwlock_timedwrlock 3 , 106.Xr pthread_rwlock_unlock 3 107.Sh STANDARDS 108The 109.Fn pthread_rwlock_timedrdlock 110function is expected to conform to 111.St -p1003.1-96 . 112.Sh HISTORY 113The 114.Fn pthread_rwlock_timedrdlock 115function first appeared in 116.Fx 5.2 . 117